Abstract 5421: Calcium/Redox Sensitive Tyrosine Kinase Pyk2 Aggravates Myocardial Ischemia by Promoting Inflammatory Reactions and Cell Apoptosis
Background: Cardiovascular system is continuously exposed to various stresses. Redox, Ca(2+)-sensitive tyrosine kinase Pyk2 is activated by stress stimuli, including inflammatory cytokines, mechanical stresses, hypoxia, and Reactive Oxygen Species (ROS), and regulates cell survival, cell motility, and cytokine induction, suggesting that Pyk2 reacts to cardiovascular stresses and maintains homeostasis. We here investigated the role of Pyk2 in ischemic myocardium and cardiac remodeling.
Methods: We analyzed 9 weeks-old male Pyk2-deficient (Pyk2−/−) and control (WT) mice with myocardial infarction (MI) model by coronary ligation. Infarct size and remodeling was evaluated by echocardiography and pathologic analyses. Furthermore, molecular analyses of heart samples and murine cardiomyocytes were performed.
Results: At 4 weeks after MI, infarct sizes of the Pyk2−/− hearts were smaller than the WT (46.8%:56.8%, p<0.01, n=12). In the Pyk2−/− mice, left ventricular end-diastolic dimensions (LVDd) were smaller and fractional shortenings (%FS) were greater, compared with the WT (LVDd 4.39mm:4.91mm, %FS 17.4%:14.8%, p<0.05, n=12) by echocardiography. Inflammatory cell infiltration and TUNEL-positive cell apoptosis in the ischemic border zones decreased to 83%, 72% of the WT, respectively (each p<0.05, each n=5). Induction of inflammatory cytokines including MCP-1 and TNF-alpha in the ischemic regions was significantly attenuated in the Pyk2−/− mice. There was little difference between them in angiogenesis. In the Pyk2−/− cardiomyocytes, the number of apoptotic cells under 1%-oxygen with 0.5% serum for 24 hours reduced to 71% of the WT (each p<0.05, n=5). Expression of GRP-78, an ER (endoplasmic reticulum)-chaperon, after 12 hours-serum deprivation was markedly up-regulated in the Pyk2−/− cardiomyocytes. Hypoxia-induced ROS-production was 48% lower (p<0.05, n=5) with DCF-staining. Phosphorylation of Src and Akt and HIF1-alpha-accumulation were decreased by Western blot analysis, and VEGF-mRNA level was reduced by RT-PCR. Consistently, in the ischemic myocardium of the Pyk2−/− mice, vascular permeability was up-regulated.
Conclusion: Pyk2 promotes cardiac remodeling by promoting inflammatory reactions and apoptosis.